E85Forum.com

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.

Has anyone experiencing this? When my engine is at cruise rpm, (2000-2300rpm) there is a poping sound coming from the exhaust. I've lost my access to my son's LM-1, so I've more or less been changing things to see if it has any effect. I've gone richer, leaner, changed timing, changed advance springs, change IFR's and experimented with emulsions bleeds, all with little or no difference being noticed. Plugs look gray. Heat band is at the bend. Top of plug has light soot about 3/4 around. Above 2300 rpm, it smooths out real nice. Performance is there. I'm happy with that, but the cruise popping is bugging the heck out of me. Any of you got any suggestions? Bare in mind, this is mainly a cruiser, not a race car. Street driveablility is a big concern.
Thanks,
Larry
_________________
'68 Roadrunner 440 4 speed
3900#street cruiser.
Best et 11.60 @ 120mph with 1.62 60' time

Eric68 · Joined: 01 Nov 2007 Posts: 185

If the engine feels like it is running OK, but just popping look for an exhaust leak. Air leaking into the exhaust can cause this. Had this issue with mine and tried switching everything from ignition to carb (even fuel).

If the engine is not running OK (like it is a surge or a misfire) then there is some tuning to do. Low electrical system voltage can cause this too.
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E85 powered 68 Camaro street car
Best ET 10.05 @ 132 MPH

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.

The engine seems to be lacking power at these rpms. Like I have to give it more "gas" to keep moving. My vacuum guage reads good though. It doesn't have any exhaust leaks. This isn't the type of popping I'm hearing. It is defininetly coming out of the tail pipes. Like a rapid putt , putt, putt, putt, but rpm related. The more rpm, the faster the popping. No smoke, doesn't use oil, plugs look good. Above or below this rpm range the engine is smooth. Maybe it's just the cam profile and I have to live with it. I don't know! At 1800 rpm, the engine is smooth. At 3000 rpm and higher, it is smooth. The thing is, it that it wasn't like this before I converted to E-85. I'm thinking it has to do with something in the carb. I just don't know how to fix it.
_________________
'68 Roadrunner 440 4 speed
3900#street cruiser.
Best et 11.60 @ 120mph with 1.62 60' time

Drag Chevette · Joined: 18 Sep 2007 Posts: 207

I would say it is the transition curcuit or possibly the powervalve curcuit.....

post your specs again and let me see what you have and I will throw out some suggestions....

also, whats your idle vacuum in gear.....???

might be as simple as an IFR change to possibly a PV change.

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.

Here goes:
Quick Fuel 1050 AN carb
Pri jet #92
Sec jet .102" drilled
P.V. 6.5 pri plugged sec.
P.V.C.R. .067"
Pri nozzle .045"
Sec nozzle .045"
acc. pump 50cc pri/sec
pump cams brown
IAB's .063"
HSAB's .029"
Emulson
bleeds
top plugged
sec .028"
third plugged
bottom .028"
IFR's pri/sec .041"
Needle seat .130 stainless

Idle vacuum in neutral is 9" at 1250rpm
_________________
'68 Roadrunner 440 4 speed
3900#street cruiser.
Best et 11.60 @ 120mph with 1.62 60' time

Eric68 · Joined: 01 Nov 2007 Posts: 185

Gotcha -- I am in agreement with drag chevette. Probably an IFR adjustment. Probably bigger, but let's see what you got first.

The funny thing about E85 is that it will pop and sputter when it is very rich, similar to a lean pop on gasoline.

That 2,000-3,000 RPM range is the area where the mains start to kick in and the transition circuit starts to peter out. They overlap somewhat so if one of the two circuits is dropping out too quick or coming on too slow, etc. you can have the problem you describe. Sounds like once you are fully on the main circuit you are alright . . .
_________________
E85 powered 68 Camaro street car
Best ET 10.05 @ 132 MPH

Drag Chevette · Joined: 18 Sep 2007 Posts: 207

I see three things that I didnt like about your specs....

1.P.V.C.R. .067", = I would like to see this up around the high .080s low .090s.....most the carb builders I talk to are anywhere from .083 to .093.....I personally like to go larger as it helps control rpm when the cars on the transbrake...footbrake may like smaller....???

2.IFR's pri/sec .041", = .039 or maybe even .037....this is where I think your off idle pop is coming from....your fat.
the IAB air will mix with the fuel from the mainwell thats drawn past the IFR.....this emulsified air will then travel through the channel that is restricted by the Idle air mix....if your fat here you would be fat during the transition or just off idle.....take the IFR down to a .039 and see if the popping gets better........if its worse then you may be lean....then shoot it up to a .045.

3. P.V. 6.5 pri plugged sec. = 5.5 or even a 4.5, secondary plugged.

Im sure eric may have a different view on this, which could be a good thing.....more options to choose from.

so dont take what I say as the way to fix it...as it is my opinion based off testing.

keep us posted on what you do and the results.

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.

Thanks for the suggestions. I appreciate the help.
Last night I upped the IFR's only. Went from .041" to .046". This caused the popping to drop below 2000 rpm. Now I have a nice idle at 1200 rpm, slowly feeding the gas (in my garage) the engine will begin to run rough up to 2000 rpm, then smooth out. Idle mixture screws were taken in, 1/4 turn. Now at 1/2 turn, out (all 4). This I don't like, but any further either way and the engine either runs rich or stalls.
The carb gas IFR's were already at .035" before the conversion.Upping 25% would make them .044". This is what I used for the formula when I did the conversion. I've since made adjustments for best reads using an LM-1. Like I said before. I don't have access to the LM-1 at this time. So I've got to do this by "seat of the pants".
I going to take the car for a ride tonight to see how it reacts on the road before I change anything else.
Thanks again for the help.
Larry
_________________
'68 Roadrunner 440 4 speed
3900#street cruiser.
Best et 11.60 @ 120mph with 1.62 60' time

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.

I took the car for a ride last night. The popping is still there but now between idle and 1800 rpm. I notice the off idle transistion is much cleaner and smoother with the bigger IFR's.
I made a few other changes. I replaced the PV with a 4 door 3.5. I also increased the PVCR to .078". I also experimented with air bleeds. All of the changes were made "one at a time" so I could get a real good feel as to what was happening. After the PV and .078" changes I notice a slight hesitation when the secondaries kicked in. I may go back to the 6.5 PV.
No black smoke. When I change LSAB's, I noticed that the poping would move opposite of the size of the bleed. Like if I used a .055" the poping would move higher in the rpm band. When I went the other way, like a .073" the poping would move closer to idle rpm. Right now I'm at .046" IFR's, .063" LSAB, 3.5 PV. with the PVCR at .078". Idle is at 1200rpm. Mixture screws are out 3/4 turn. Poping is at 1400 to 1800 but not as bad as it was. Just noticable to my finiky ear.
Question: Any chance of plug gap having an effect on this popping? Im running an MSD 6AL with the plugs gapped at .045".
Thanks for any help,
Larry
_________________
'68 Roadrunner 440 4 speed
3900#street cruiser.
Best et 11.60 @ 120mph with 1.62 60' time

Eric68 · Joined: 01 Nov 2007 Posts: 185

Interesting results with the LSAB. Counter-inutuitive really.

I would go bigger yet on the IFR and stay with the smaller LSAB. I'm guessing the smaller bleed is pulling hard enough on the IFR to satisfy low RPM requirements but is running out of steam at the top end of the transition RPM range.

I doubt plug gap has anything to do with it, but going down to .035 couldn't hurt.
_________________
E85 powered 68 Camaro street car
Best ET 10.05 @ 132 MPH

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.

Thanks for the suggestions. The thing that I notice with making changes to the IFR's is how much they affect the mixture screws. I know that the mixture screws are actually volumn screws, but every time I increase the IFR's, I have to reduce the volumn, (lean out the mixture screws). I'm not real comfortable with where I'm at right now. I like to be at least 1 full turn out, but I'm at 3/4" turn at this time. If I increase the IFR's, I'll probably be less than 1/2 turn out. Then I'm looking at drilling the throttle blades and I don't want to do that.
Larry
_________________
'68 Roadrunner 440 4 speed
3900#street cruiser.
Best et 11.60 @ 120mph with 1.62 60' time

Drag Chevette · Joined: 18 Sep 2007 Posts: 207

68LAR · Joined: 22 Feb 2008 Posts: 34 Location: South Park, Pa.